The present invention relates to improvements in low-dose hypodermic syringes and more particularly to the joint connection to attach the needle assembly to the barrel of the syringe.
In low-dose syringes, parts are normally small while generated forces during injection are comparatively high. Problems have been experienced in initially creating a liquid tight seal between the parts of the needle assembly and syringe barrel and maintaining it during removal of the needle sheath and while injecting the contained liquid. When dealing with syringes of 1/2 cc and less capacity, accuracy in amount of liquid injected becomes critical in assuring proper medication and therapy.
The standard luer connection in frequent use today is not entirely satisfactory for low-dose syringes and also has an internal volume significantly beyond the main barrel chamber so that the syringe must be filled with excess medicament to compensate for this volume when measuring dosage. After administration, this residual volume of medicament remains in the syringe tip and needle hub lumen. When two or more medicaments are measured in the same syringe, the excess or residual volume will create an error of their relative ratio in the resultant mixture.